U.S. patent application number 11/250481 was filed with the patent office on 2006-04-27 for optical information reproduction apparatus and optical information reproduction method.
This patent application is currently assigned to Sony Corporation. Invention is credited to Isao Ichimura, Tsutomu Maruyama.
Application Number | 20060087937 11/250481 |
Document ID | / |
Family ID | 36206051 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060087937 |
Kind Code |
A1 |
Maruyama; Tsutomu ; et
al. |
April 27, 2006 |
Optical information reproduction apparatus and optical information
reproduction method
Abstract
An optical information reproduction apparatus for reproducing a
recording signal by irradiating a light beam onto a recording
surface of an optical information recording medium having at least
two information recording layers and by receiving reflected light
of the light beam is provided. The optical information reproduction
apparatus includes an extraction section for extracting an envelope
signal of a reproduction signal when the reproduction signal
reproduced by focusing the light beam onto one information
recording layer in the plural information recording layers has been
modulated by interlayer crosstalk from another information
recording layer; and a distortion correction section for correcting
the distortion of the target reproduction signal caused by the
interlayer crosstalk by gain-adjusting the reproduction signal
containing DC components so that the envelope signal becomes
constant.
Inventors: |
Maruyama; Tsutomu; (Chiba,
JP) ; Ichimura; Isao; (Tokyo, JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING
1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Assignee: |
Sony Corporation
Tokyo
JP
141-0001
|
Family ID: |
36206051 |
Appl. No.: |
11/250481 |
Filed: |
October 17, 2005 |
Current U.S.
Class: |
369/47.1 ;
369/59.1; G9B/20.012 |
Current CPC
Class: |
G11B 20/10027 20130101;
G11B 2020/1288 20130101; G11B 2007/0013 20130101; G11B 20/10203
20130101; G11B 2220/2541 20130101 |
Class at
Publication: |
369/047.1 ;
369/059.1 |
International
Class: |
G11B 5/09 20060101
G11B005/09 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2004 |
JP |
P2004-309956 |
Claims
1. An optical information reproduction apparatus for reproducing a
recording signal by irradiating a light beam onto a recording
surface of an optical information recording medium having at least
two information recording layers and by receiving reflected light
of the light beam, the optical information reproduction apparatus
comprising: extraction means for extracting an envelope signal of a
reproduction signal when the reproduction signal reproduced by
focusing the light beam onto one information recording layer in the
plural information recording layers has been modulated by
interlayer crosstalk from another information recording layer; and
distortion correction means for correcting the distortion of the
target reproduction signal caused by the interlayer crosstalk by
gain-adjusting the reproduction signal containing DC components so
that the envelope signal becomes constant.
2. The optical information reproduction apparatus according to
claim 1, further comprising: determination means for determining
whether the optical information recording medium has plural
information recording layers or a single information recording
layer on the basis of a reading from the information recording
layer; and control means for allowing the extraction means and the
distortion correction means to operate when it is determined by the
determination means that the optical information recording medium
has plural information recording layers and for otherwise allowing
signal processing means to perform signal processing without
allowing the extraction means and the distortion correction means
to operate.
3. The optical information reproduction apparatus according to
claim 1, further comprising signal processing means for obtaining a
reproduction result by performing signal detection on the basis of
a reproduction signal after distortion caused by the interlayer
crosstalk is corrected by the distortion correction means.
4. An optical information reproduction method for reproducing a
recording signal by irradiating a light beam onto a recording
surface of an optical information recording medium having at least
two information recording layers and by receiving reflected light
of the light beam, the information reproduction method comprising
the steps of: extracting an envelope signal of a reproduction
signal when the reproduction signal reproduced by focusing the
light beam onto one information recording layer in the plural
information recording layers has been modulated by interlayer
crosstalk from another information recording layer; and correcting
the distortion of the target reproduction signal by the interlayer
crosstalk by gain-adjusting the reproduction signal containing DC
components so that the envelope signal becomes constant.
5. An optical information reproduction apparatus for reproducing a
recording signal by irradiating a light beam onto a recording
surface of an optical information recording medium having at least
two information recording layers and by receiving reflected light
of the light beam, the optical information reproduction apparatus
comprising: an extraction section extracting an envelope signal of
a reproduction signal when the reproduction signal reproduced by
focusing the light beam onto one information recording layer in the
plural information recording layers has been modulated by
interlayer crosstalk from another information recording layer; and
a distortion correction section correcting the distortion of the
target reproduction signal caused by the interlayer crosstalk by
gain-adjusting the reproduction signal containing DC components so
that the envelope signal becomes constant.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present invention contains subject matter related to
Japanese Patent Application JP 2004-309956 filed in the Japanese
Patent Office on Oct. 25, 2004, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical information
reproduction apparatus and an optical information reproduction
method, and it is suitable for use in, for example, an optical
information recording and reproduction apparatus for recording and
reproducing information on an optical disc having plural
information recording layers.
[0004] 2. Description of the Related Art
[0005] In recent years, in optical information recording and
reproduction apparatuses for recording and reproducing information
on a recording medium such as an optical disc, a technique for
making recording information into a higher density by a shortening
of the wavelength of a light source and by a higher aperture number
of an objective lens has been proposed. For example, a two-layer
disc having a recording capacity exceeding 23 Gbytes per layer as a
result of using an objective lens with the aperture number 0.85 and
a bluish purple semiconductor laser of a wavelength 405 [nm] has
been standardized as a "Blu-ray Disc (trademark)". Furthermore, in
recent years, as the density of recording information becomes
higher, a lot has been reported about multilayer optical discs for
optically reading, from one side, recording information layers that
are formed in plural layers.
[0006] When the recording information of a particular information
recording layer Ln within such a multilayer optical disc is
reproduced, if the distance between adjacent layers is sufficiently
large, influences due to the leakage of signals (hereinafter,
referred to as "interlayer crosstalk") from a plurality of
information recording layers other than the information recording
layer Ln are small, and the reproduction characteristics of a RF
signal does not particularly pose a problem.
[0007] The smaller the interlayer distance, the larger the
interlayer crosstalk, and the RF signal is deteriorated. The
smaller interlayer distance is caused by a limitation of the
distance from the disc surface to each information recording layer
due to the number of layers of a multilayer optical disc, the
correction range of an expander for correcting spherical aberration
caused by the difference in the distance from the disc surface to
each information recording layer by a higher aperture number of an
objective lens, an inclination margin between the objective lens
and the disc, and defects such as scratches and fingerprints.
[0008] As a technique for reducing such interlayer crosstalk, there
is a known pickup device in which the standardized detector size of
an optical detector is optimized (refer to, for example, Japanese
Unexamined Patent Application Publication No. 2002-25098).
SUMMARY OF THE INVENTION
[0009] In a pickup device having such a configuration, in order
that the stability of a focus servo and the mounting accuracy and
reliability of an optical detector do not deteriorate, it is
difficult to reduce the standardized detector size to less than a
particular degree. As a result, when the layer spacing is narrow to
such a degree of approximately 10 [.mu.m] to 20 [.mu.m], the RF
signal is modulated by interlayer crosstalk, and distortion is
caused to occur. Thus, there is a problem in that, when a
binarization is performed on the basis of the RF signal in which
the distortion occurred, it is difficult to correctly reconstruct
the reproduction result.
[0010] The present invention has been made in view of the above
points. It is desirable to provide an optical information
reproduction apparatus that obtains an accurate reproduction result
by removing in advance the distortion caused by interlayer
crosstalk of a reproduction signal when information on an optical
information recording medium having plural information recording
layers is reproduced.
[0011] According to an embodiment of the present invention, in an
optical information reproduction apparatus for reproducing a
recording signal by irradiating a light beam onto a recording
surface of an optical information recording medium having at least
two information recording layers and by receiving reflected light
of the light beam, an envelope signal of a reproduction signal is
extracted when the reproduction signal reproduced by focusing the
light beam onto one information recording layer in plural
information recording layers has been modulated by interlayer
crosstalk from another information recording layer, and the
distortion of the target reproduction signal by the interlayer
crosstalk is corrected by gain-adjusting the reproduction signal
containing DC components so that the envelope signal becomes
constant. Thus, even when the influence of distortion due to
interlayer crosstalk appears in the reproduction signal from the
optical information recording medium having plural information
recording layers, the influence of the distortion can be prevented,
and the reproduction result can be reconstructed without errors on
the basis of a reproduction signal before the influence due to the
interlayer crosstalk is received.
[0012] In an embodiment of the present invention, the optical
information reproduction apparatus further includes determination
means for determining whether the optical information recording
medium has plural information recording layers or a single
information recording layer on the basis of a reading from the
information recording layer and control means for allowing
extraction means and distortion correction means to operate when it
is determined by the determination means that the optical
information recording medium has plural information recording
layers and for otherwise allowing signal processing means to
perform signal processing without allowing the extraction means and
the distortion correction means to operate. Thus, only when the
optical information recording medium has plural information
recording layers, the influence of distortion due to interlayer
crosstalk can be removed, and a useless operation for removing the
influence of distortion due to interlayer crosstalk even when the
optical information recording medium has a single information
recording layer can be prevented from being performed.
[0013] According to the embodiments of the present invention, it is
possible to realize an optical information reproduction apparatus
and an optical information reproduction method which can remove the
influence of distortion even when the influence of distortion due
to interlayer crosstalk appears in the reproduction signal from the
optical information recording medium having plural information
recording layers which can reconstruct a reproduction result
without errors on the basis of a reproduction signal before the
influence due to the interlayer crosstalk is received.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic diagram showing the configuration of
an optical pickup;
[0015] FIG. 2 is a schematic block diagram showing the circuit
configuration of an optical information recording and reproduction
apparatus;
[0016] FIG. 3 is a schematic diagram illustrating AGC with respect
to RF signal containing DC components;
[0017] FIG. 4 is a schematic diagram illustrating AGC with respect
to RF signal after AC coupling; and
[0018] FIG. 5 is a schematic block diagram showing the
configuration of an AGC circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] An embodiment of the present invention will now be described
in detail below with reference to the drawings.
(1) Configuration of Optical Pickup
[0020] In FIG. 1, reference numeral 1 denotes an optical pickup as
a whole. The optical pickup 1 converts light LD1 emitted from a
semiconductor laser diode 2 into parallel light by a collimator
lens 3, causes the parallel light to pass through a 1/2 wavelength
plate 4, causes it to pass through a diffraction grating 5 for
generating a side spot used to compute a tracking control error
signal, and thereafter separates it into transmitted light and
reflected light by a polarized light beam splitter 6. This spectral
ratio can be adjusted by rotating the 1/2 wavelength plate 4.
[0021] The light transmitted through the polarized light beam
splitter 6 passes through a wavefront conversion element 7, which
is formed of an expander or a liquid-crystal optical element, for
correcting spherical aberration caused by a thickness error of a
cover layer 11a1 and cover layers 11a2 to 11an from the disc
surface of an optical disc 10 to an information recording layer,
passes through a 1/4 wavelength plate 8 for converting
linearly-polarized light into circularly-polarized light, and
thereafter is collected onto the optical disc 10 by a
high-aperture-number objective lens 9.
[0022] The light reflected by the polarized light beam splitter 6
is guided to a light-receiving element 12 for detecting emission
light output by the light-collecting lens 11, and the detection
result of the light-receiving element 12 for detecting emission
light output is used to control the laser power of the emitting
light LD1 from the semiconductor laser diode 2.
[0023] On the other hand, the reflected light from the optical disc
10 passes through the high-aperture-number objective lens 9, the
1/4 wavelength plate 8, and the wavefront conversion element 7, and
is reflected by the polarized light beam splitter 6. Thereafter,
the light is guided to the detection light path. In this case, an
astigmatism method is used as a focus error control method, and
also, a differential push-pull method is used as a tracking error
control method. The converging light that has passed through a
light-collecting lens 13 and a multi-lens 14 enters a
light-receiving element 15 for detecting a servo error signal and a
RF signal, whereby it is photoelectrically converted.
[0024] The light-receiving element 15 for detecting a servo error
signal and a RF signal outputs the light-receiving signal obtained
by photoelectrically converting the converging light into a circuit
at a subsequent stage. Here, the light-receiving surface of a main
beam within the light-receiving element 15 for detecting a servo
error signal and a RF signal is formed of a four-division optical
detector.
(2) Configuration of Optical Information Recording and Reproduction
Apparatus
[0025] As shown in FIG. 2, an optical information recording and
reproduction apparatus 20, which uses the optical pickup 1 shown in
FIG. 1, performs a computation process using a matrix computation
circuit 21 on the basis of a light-receiving signal read from the
optical disc 10 by the optical pickup 1, in order to generate a
focus control error signal, a tracking control error signal, a
spherical aberration control error signal, and a RF signal for
signal processing, and sends the focus control error signal, the
tracking control error signal, the spherical aberration control
error signal, and the RF signal for signal processing to a servo
signal processing circuit 22.
[0026] In the servo signal processing circuit 22, gain adjustment
and phase compensation are performed. Thereafter, by controlling
the rotational speed of a spindle motor 25 via a spindle motor
control circuit 23 and by controlling an actuator (not shown) via
an actuator/spherical aberration control circuit 24, focus control,
spherical aberration control, and tracking control of the optical
pickup 1 are performed.
[0027] In the servo signal processing circuit 22, feeding control
in the radial direction with respect to the optical pickup 1 is
performed by controlling a motor 28 via a feeding motor control
circuit 27 by using low-frequency components of the tracking
control error signal.
[0028] On the other hand, the RF signal for signal processing
generated by the matrix computation circuit 21 is input to an AGC
(Automatic Gain Control) circuit 29 (to be described later),
distortion due to interlayer crosstalk is corrected by the AGC
circuit 29, and the RF signal is sent to a RF signal processing
circuit 30.
[0029] In the RF signal processing circuit 30, the reproduction
result is reconstructed accurately by performing waveform
equalization, a PRML (Partial Response Maximum Likelihood) signal
process, and a correction process, etc., on the RF signal from
which distortion due to interlayer crosstalk is removed.
[0030] In a LD (Laser Diode) driving circuit 26 of the optical
information recording and reproduction apparatus 20, by controlling
the emitting power of the optical pickup 1 on the basis of the
detection result obtained from the light-receiving element 12 (FIG.
1) for detecting emission light output of the optical pickup 1, the
emitting light LD1 is set at the optimum laser power.
(3) Principles for Removing Distortion Due to Interlayer
Crosstalk
[0031] For the RF signal, for example, in the case of a 17PP
modulation method, it is formed of marks and spaces whose run
length is 2 T to 8 T (T is the channel bit clock width, and 9 T
also exists but is very little). When the optical disc 10 is a
multilayer optical disc and the RF signal is affected by interlayer
crosstalk, as shown in part (A) of FIG. 3, the amplitude of the RF
signal varies, and a state is reached in which distortion such that
the envelope signal fluctuates is contained.
[0032] Within the RF signal, the signal of 8 T components whose
mark and space lengths are long is low in frequency and large in
amplitude, whereas the signal of 2 T components whose mark and
space lengths are short is high in frequency and small in amplitude
due to MTF (Modulation Transfer Function) characteristics. Although
the RF signal contains signals of 8 T components and 2 T
components, and also 3 T components, 4 T components, . . . 9 T
components, for the sake of simplicity of description, only the
signal of 8 T components and 2 T components is described below. The
waveforms of 8 T components and 2 T components in part (a) of FIG.
3 differ from the actual scale, and they are shown only
schematically.
[0033] Therefore, when the RF signal in which distortion due to
interlayer crosstalk exists is binarized by the RF signal
processing circuit 30 (FIG. 2), the amplitude of the RF signal is
varied and the envelope fluctuates. In consequence, jitter of the
RF signal (fluctuation of signal over time) becomes large, and
erroneous detection becomes frequent.
[0034] In the AGC circuit 29, in order to prevent such a situation,
the gain adjustment of the RF signal is performed in such a manner
as to correspond to an AGC control signal S1 from the control
circuit 31, so that the fluctuation that has occurred in the
envelope (in particular, the upper envelope of 8 T) as shown in
part (B) of FIG. 3 is removed and the envelope can be kept
constant.
[0035] In this case, the band of the RF signal is sufficiently
higher than the band of the distortion components of the envelope
due to interlayer crosstalk. Thus, in the AGC circuit 29, gain
adjustment is performed in the band of the envelope, so that the
envelope can be kept constant by removing the distortion thereof
without directly affecting the RF signal containing 8 T components
and 2 T components.
[0036] Here, the AGC circuit 29 is designed to adjust the amplitude
level of the RF signal in a state in which DC (Direct Current)
components are kept so as to be contained in the RF signal.
Alternatively, it is considered that the amplitude level is
adjusted with respect to the RF signal after so-called AC
(Alternating Current) coupling for removing DC components is
performed.
[0037] The reasons why the amplitude level is adjusted with respect
to the RF signal containing DC components without performing AC
coupling in the embodiment of the present invention are the
following. Since the signal of 2 T components in the vicinity of
the ground (GND) level when AC coupling is performed as shown in
parts (A) and (B) of FIG. 4 has a value in the vicinity of nearly
the 0 level, it is difficult to sufficiently increase the gain
thereof in comparison with the signal of 8 T components, for
example, even if gain adjustment is performed onto the signal of 2
T components and the signal of 8 T components at the same
magnification ratio. Also, on the minus side relative to the
ground, conversely, the distortion due to interlayer crosstalk is
increased by the gain adjustment on the lower envelope in the
signal of 8 T components. By also taking such points into
consideration, in the AGC circuit 29 according to the embodiment of
the present invention, gain adjustment is performed on the RF
signal containing DC components.
[0038] The control circuit 31 (FIG. 2) makes a determination as to
whether the optical disc 10 is a single-layer optical disc or a
multilayer optical disc during focus search on the optical disc 10
and when disc information is read during data writing, and it
outputs the AGC control signal S1 to the AGC circuit 29 only when
the optical disc 10 is a multilayer optical disc, thereby
removing-distortion of the RF signal due to interlayer
crosstalk.
[0039] When the optical disc 10 is a single-layer optical disc,
since the RF signal does not deteriorate due to interlayer
crosstalk, in the AGC circuit 29, the distortion due to interlayer
crosstalk is removed only when the AGC control signal S1 is
supplied from the control circuit 31.
(4) Configuration of AGC Circuit
[0040] In practice, as shown in FIG. 5, the AGC circuit 29 sends
the RF signal containing DC components, which is supplied from the
matrix computation circuit 21, to a peak-hold circuit 43 via a
buffer circuit 41 and a multiplier 42.
[0041] The peak-hold circuit 43 extracts an upper envelope signal
UEV 1 of the RF signal by peak-holding the RF signal containing DC
components in the band between DC and several hundred [KHz] and
sends the upper envelope signal UEV 1 to a low-pass filter circuit
44.
[0042] The low-pass filter circuit 44 allows only the upper
envelope signal UEV 1 of the RF signal extracted by the peak-hold
circuit 43 within the RF signal to pass and sends this signal to a
gain offset adjustment circuit 45.
[0043] The gain offset adjustment circuit 45 performs the
adjustment of the loop gain and offset of AGC and sends an upper
envelope signal UEV2 obtained thereby after adjustment to an adder
46.
[0044] In the adder 46, the difference between the target voltage
level supplied from a RF amplitude adjustment voltage 47 and the
voltage level of the upper envelope signal UEV2 is computed, and
the resultant computation result DH is supplied to the multiplier
42 via an AGC switching circuit 48.
[0045] Here, for the RF amplitude adjustment voltage 47, for
example, the target voltage level is set at substantially an
intermediate voltage between a relative maximum value and a
relative minimum value in the upper envelope signal UEV2 of 8 T
components (FIG. 3). Alternatively, the target voltage level may be
set to any desired voltage corresponding to a relative maximum
value and any desired voltage corresponding to a relative minimum
value.
[0046] The AGC switching circuit 48 outputs the computation result
DH from the adder 46 to the multiplier 42 only when the AGC control
signal S1 is supplied from the control circuit 31 (FIG. 2), and it
is switched by a switch so that the computation result DH is not
output to the multiplier 42 when the AGC control signal S1 is not
supplied.
[0047] In the multiplier 42, the RF signal containing DC components
from the buffer circuit 41 is multiplied by the computation result
DH supplied from the AGC switching circuit 48, so that the
fluctuation of the envelope of the RF signal receiving distortion
due to interlayer crosstalk is eliminated and the envelope is
corrected to a fixed level.
[0048] That is, in the RF signal that is finally output from the
multiplier 42, the influence of the distortion due to interlayer
crosstalk does not remain, so that erroneous reading of the signal
is prevented when the RF signal is binarized by the RF signal
processing circuit 30 at a subsequent stage.
(5) Operation and Advantages
[0049] In the above construction, even when the RF signal
fluctuates by being affected by the interlayer crosstalk, the AGC
circuit 29 of the optical information recording and reproduction
apparatus 20 can eliminate the fluctuation that has occurred in the
RF signal by applying AGC to the RF signal containing DC
components, and the envelope of the RF signal can be kept
constant.
[0050] At this time, the AGC circuit 29 performs gain adjustment so
that the upper envelope of 8 T components in the RF signal
containing DC components becomes constant on the plus side with
reference to the ground. As a result, the upper envelope of 2 T
components, the lower envelope of 2 T components, and the lower
envelope of 8 T components are made to follow the upper envelope of
8 T components so that all the envelopes of 8 T components and 2 T
components can be kept constant.
[0051] In the AGC circuit 29, AGC is applied in the frequency band
of the distortion components due to interlayer crosstalk of the
upper envelope signal of 8 T components in the RF signal. As a
result, direct influences are not exerted on the RF signal in a
frequency band far higher than the frequency band of the distortion
components due to interlayer crosstalk of the upper envelope
signal.
[0052] Therefore, in the optical information recording and
reproduction apparatus 20, since the signal can be binarized by the
AGC circuit 29 on the basis of the RF signal in which influences
due to interlayer crosstalk are eliminated, the reproduction result
can be accurately reconstructed.
[0053] According to the above construction, by applying AGC to the
RF signal containing DC components, the envelope of the RF signal
becomes constant to eliminate distortion due to interlayer
crosstalk in advance, and the reproduction result can be accurately
reconstructed on the basis of a RF signal in which the distortion
is eliminated.
(6) Other Embodiments
[0054] Although the above embodiment describes a case in which the
AGC circuit 29 is provided between the matrix computation circuit
21 and the RF signal processing circuit 30, the present invention
is not limited to this embodiment, and the AGC circuit 29 may be
provided between the matrix computation circuit 21 and the servo
signal processing circuit 22. As a result, in the optical
information recording and reproduction apparatus 20, servo control
can be performed accurately.
[0055] Although the above embodiment describes a case in which the
upper envelope signal UEV 1 is extracted on the basis of the peak
level of the 8 T components of the RF signal by the peak-hold
circuit 43 of the AGC circuit 29 and gain adjustment is performed
on the upper envelope signal UEV 1, the present invention is not
limited to this embodiment. In addition, the lower envelope signal
may be extracted on the basis of the bottom level, and gain
adjustment may be performed on the RF signal on the basis of the
lower envelope signal.
[0056] Although the above embodiment describes a case in which the
AGC circuit 29 according to the embodiment of the present invention
is incorporated in the optical information recording and
reproduction apparatus 20, the present invention is not limited to
this embodiment. In addition, the AGC circuit 29 according to the
embodiment of the present invention may be incorporated in a
read-only optical information reproduction apparatus.
[0057] Although the above embodiment describes a case in which the
optical information recording and reproduction apparatus 20 serving
as an optical information reproduction apparatus is formed of the
peak-hold circuit 43 serving as extraction means, the gain offset
adjustment circuit 45 serving as distortion correction means, the
adder 46, the RF amplitude adjustment voltage 47, and the
multiplier 42, the present invention is not limited to this
embodiment. In addition, the optical information reproduction
apparatus may be formed of other various types of circuit
configurations.
[0058] The optical information reproduction apparatus and the
optical information reproduction method according to the
embodiments of the present invention can be applied to various uses
in which, for example, when influences of interlayer crosstalk
occur in the reproduction signal of the multilayer optical disc,
the influences are eliminated and reproduction is performed
accurately.
[0059] It should be understood by those skilled in the art that
various modifications, combinations, subcombinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *